Copper/iron/aluminm alloys



May 21, 1968 s. HARPER ET AL 3,384,517

COPPER/IRON/ALUMINUM ALLOYS Filed Dec. 14, 1965 Cu) 1, 0 40 so so 70 a0 90 OCCu/A! Maj/Al Weight ber cent.

oCCu/Al X Cu/Al United States Patent 3,384,517 COPPER/ IRON/ ALUMINUM ALLOYS Sydney Harper, Ross McKenzie Anderson, and Richard John Lane Eborall, London, England, assignors to National Research Development Corporation, London, England, a British corporation Filed Dec. 14, 1965, Ser. No. 513,786 Claims priority, application Great Britain, Dec. 22, 1964, 52,152/ 64 7 Claims. (Cl. 148-32) ABSTRACT OF THE DISCLOSURE Copper-iron-aluminum alloys comprising a matrix of a copper-rich solid solution phase containing about -10 percent by weight of aluminum, said matrix containing in the form of fibre, an iron-rich solid solution phase containing about 10-20 percent by Weight of aluminum, have been found to provide unexpectedly high tensile strengths. The desired fibre form of the iron-rich solid solution in the alloy may be obtained by subjecting a casting of the 'alloy to a hot working process such as an extrusion or a rolling treatment, preferably followed by a cold-working process.

This invention relates to copper-iron-aluminum. alloys and according to the invention such an alloy comprises a matrix of a copper-rich solid solution phase containing about 5-10 percent by weight of aluminum and said matrix contains, in the form of fibre, an iron-rich solid solution phase containing about 10-20 percent by weight of aluminum.

The alloy according to the invention should preferably comprise not less than 20 percent and not more than about 50 percent by weight of iron and preferably the total aluminum content should not be greater than about percent, nor less than about 5 percent by weight.

It will be understood, of course, that the fibrous structure need not be confined to actual fibres-it may be formed as a multiplicity, for example, of platelets or the like; but the form of the structure will generally be characterised by the presence of particles of the ironrich solid solution phase having at least a dimension longitudinally which is many times greater than that transversely.

The accompanying drawing shows a phase diagram attributed to Bradley 'and Goldschmidt (J. In-st. Metals, 1939, 65 389) and represents the condition of slowly cooled alloys in the copper-iron-aluminum system. Since changes are slow at temperatures below 500 C., the diagram has been generally considered to correspond to equilibrium at about 500 C. Reference to this diagram shows that, at temperatures near 500 C. and below, an alloy according to the invention should preferably be of substantially one of the compositions represented within the hatched area. It is seen that there is no tendency for the gamma copper-aluminum phase to form in the alloys according to the invention, except near the upper limits of aluminum content. In fact, as shown in the diagram, it appears that the upper limit of aluminum content can be as high as about 15 percent by weight, when iron is present in its higher concentrations.

However, since the gamma copper-aluminum phase is brittle, it will probably be found desirable, from the point of mechanical properties, to ensure that the aluminum content is carefully controlled so as not to exceed this upper limit, if at all, by more than a very small amount, and thereby to avoid the presence of more than a negligible quantity of gamma copper-aluminum phase inclusions.

3,384,517 Patented May 21, 1968 "ice Alloys in accordance with the invention will almost invariably initially be in the form of castings and may be prepared using techniques similar to those used for the preparation of the well-known aluminum-bronze alloys, having regard to the somewhat higher melting point (i.e. in the range up to 1375 C., compared with about 1080 C. for the aluminum-bronzes) and a longer freezing range. The microstructure, in the as-cast condition, of alloys in accordance with the invention, consists of dendrites 'of the iron-rich solid solution phase in the matrix of a copper-rich phase, and it would appear that the iron-rich solid solution phase is the Fe Al phase in the binary Fe-Al system with the addition of about 5-10 (Weight) percent of copper in solution. It is essential to work these cast alloys so that the iron-rich solid solution phase becomes elongated to achieve the desired fibre form. While it may be possible in some cases to procure a satisfactory form by cold-working the cast alloy, as, for example, by hydrostatic extrusion, it will probably be best achieved by a hot-working process, such as an extrusion or a rolling treatment; it is 'a fact, however that the fibrous structure can be developed still further by cold-working following such hot-working process.

Tests have been made on alloys in which the copperiron ratio is of the order of 1:1 and 1:2 and the results are shown in the accompanying Tables I, II and III.

TABLE I.MECHANIOAL PROPERTIES OF ALLOY 61CU- 26FE-13AL 1 Approximating to 0.5% proof stress.

TABLE IL-MECHANICAL PROPERTIES OF ALLOY 59CU- 33FE8-AL Approx. Tensile Elon- Condition yield, strength, gation,

tons/in. tons/in. percent Extruded 16:1 at 950 C 32. 2 44.0 29 Extruded 16:1 at 850 C. and cold rolled into strip reduction 67.0 3 Extruded 16:1 at 850 C., cold-rolled (80% reduction) annealed 5 hrs. at 520 C. and water quenched 48. 2 11 l Approximating to 0.5% proof stress.

TABLE III-MECHANICAL PROPERTIES OF ALLOY 45CU- 45FE-10AL Approx. Tensile Elon- Condition yield, strength, gation, tons/in. tons/in. percent Extruded 9:1 at 900 C 42. 2 52. 6 19 Extruded 16:1 at 950 C 2 23. 9 51. 0 13 Extruded and hot-rolled both at 950 0. overall reduction :1 52. 0 Extruded 9:1 at 900 C. cold-rolled into strip reduction 50% 72. 9 Extruded 9:1 at 950 C. ld-swaged 8 reduction of area 80% 65. 5 73. 5 7. 5 As above but annealed 4 h at 800 0., furnace cooled 45.0 55. 6 17.5

1 Approximating to 0.5% proof stress. 2 0.1% proof stress.

Reference to Table 1 indicates that 1t is possible for alloys within the range of the present composition to be brought into condition by subjecting a cast ingot to a 50-90 percent reduction by uni-directional hot-rolling at temperatures above 500 C. to exhibit yield strengths some 50 percent higher than those normally attributed to aluminum bronzes in which the iron content is of the order of only up to about 6 (weight) percent; typical figures for these aluminum bronzesare tensile strength 40-44.5 tons/sq. in. and elongation of 12-20 percent. Extrusion in ratios of about 9:1 upwards at temperatures round about 800 C.900 C. also produces material with properties comparable with those obtained by straight forward hot-rolling as reference to the tables shows. It is found, moreover, that even higher tensile strength can be achieved by subsequently cold-working the extruded material, such as by rolling or swaging into strip or bar, and the order of results to be expected from such further working is, again, indicated in the tables. The recommended treatment for best results would, in fact, probably be an extrusion treatment followed by cold-working, such as rolling, swaging or drawing, and, if the comparatively low elongation figures are not entirely acceptable for certain applications, the ductility may be improved, though at the expense of highest tensile strengths, -by annealing treatment; this is illustrated in the case of alloys 45Cu- 45 Fe-1OA1 and 59Cu-33Fe-8Al in Tables II and III.

In the present alloys it is found that the hardness of the iron-rich phase, although substantially greater than that of the copper-rich matrix phase is still of the same order of magnitude; for example, in one alloy, the hardness of the iron-rich phase was found to be 360 Vickers Hardness, while that of the copper-rich phase was 200. In spite of the fibrous nature of the former phase, therefore, the alloys would appear not to be true, so-called, fibre-reinforced alloys for, in the latter alloys, it is usual for the material of the fibres to be at least of an order or so higher in hardness than the matrix material. The high material strengths attained by the present alloys are, therefore, somewhat unexpected.

It does happen that short transverse strengths of some of the present alloys may be only a fraction, possibly as low as a third, of the longitudinal strengths and it would, therefore, appear that the latter high values are the results of the fibrous form of the iron-rich phase in each case.

Certainly, in a room temperature notched-bar test of the Izod type of an alloy of composition similar to that of Table II, where the specimen remained only partially broken, the material showed a well-developed fibrous structure. Impact values of these alloys in general, however, vary over a wide range, depending upon the structure of the material.

It will be understood that, while the proportions of the principal constituents remain within the ranges given, small amounts of other constituents may be present, possibly as normal impurities but possibly also from the point of small additions, for example, to strengthen the fibrous iron-rich solid solution phase or to improve its corrosion resistance. Such additions will be evident to those skilled in the art and, in consequence, are not detailed here.

We claim:

1. A copper-iron-aluminum alloy comprising a matrix of a copper-rich solid solution phase containing about 5-10 percent by weight of aluminum, said matrix containing in the form of fibre, an iron-rich solid solution phase containing about 10-20 percent by weight aluminum, said alloy comprising not less than 20% and not more than by weight of iron and having a total aluminum content of not greater than about 15% and not less than about 5% by weight.

2. A process for preparing the alloy of claim 1 which comprises'hot working a casting of a copper-iron-aluminum alloy comprising a matrix of a copper-rich solid solution phase containing about 5-10 percent by weight of aluminum, said matrix containing an iron-rich solid solution phase containing about 10-20 percent by weight of aluminum, said alloy comprising not less than 20% and not more than 50% by weight of iron and having a total aluminum content of not greater than 15 and not less than about 5% by weight, to elongate said iron-rich solid solution into the form of fibre.

3. The process of claim 2 wherein the hot working comprises extrusion at a temperature above 500 C.

4. The process of claim 3 wherein the extrusion is at a ratio of at least about 9:1.

5. The process of claim 3 wherein the fibre of the iron-rich solid solution phase is further developed by a cold-working operation.

6. The process of claim 5 wherein the said cold-working comprises a cold-rolling treatment.

7. The process of claim 5 wherein said cold-working comprises a cold-swaging treatment.

References Cited UNITED STATES PATENTS 1,452,232 4/1923 Faiser -162 OTHER REFERENCES The Journal of the Institute of Metals, 1939, Bradley et al., pp. 389-401.

CHARLES N. LOVELL, Primary Examiner.

HYLAND BIZOT, Examiner. 

